The methods and apparati described herein relate generally to power supply systems, and, in particular, to methods and apparati for providing battery-based power to a load, by way of a power supply system including a multiple cell battery pack or module.
The operation of certain electronic devices, such as implanted heart pumps, requires continuous application of power, i.e., voltage and current, derived from an implanted battery source. Typically, the battery source is a battery module including a set of interconnected rechargeable battery cells. It is often critical for such devices that the required power is delivered in spite of battery cell failures which might occur during the operation of the base electronic, or load, device.
Some known power supply systems for meeting the continuous, and fault-tolerant power requirements of such electronic devices, consist of a battery pack including multiple interconnected battery cells as a primary source of power, and a control circuit that controls ancillary operations relating to the battery cells, such as control of re-charging rate and discharge rate and the like. Typically, the control circuit provides a protection for the power supply system, so that neither the power supply system, nor a load device coupled thereto, is damaged in the event of one or more batteries cell failures. In some known power supply systems, the control circuit shuts down the power supply system when one or more battery cells fail to operate properly, including the shutdown of both the failed battery cells as well as remaining still-functional battery cells. Such a power supply system is not acceptable where a continuous supply of power is critical and interruptions cannot be tolerated, and where direct access to the battery cells for replacement, is not practical (e.g., certain military applications, satellite applications, and implanted medical device applications, and the like).
In some other known power supply systems having a multiple cell battery pack for primary power, a secondary (redundant) battery pack packaged in or near the primary power pack, provides power to a load coupled thereto, when the primary battery pack fails to provide sufficient power. For such systems, a control circuit of the power supply system, generally detects a failure of the one or more cells of the primary battery pack, and upon such detection, switches operation to the redundant battery. The aggregate number of battery cells in such a power supply system is greater than the number of battery cells used at any given moment, which increases cost and reduces efficiency. Such a power supply system is not acceptable where a continuous supply of power is critical and interruptions cannot be tolerated, and where there is no practical volume for the storage of the redundant battery pack.
Accordingly, a need exists for an apparatus and/or method to enable a multiple battery cell-based power supply system to provide power continuously to a load device, in the event of a battery cell failure, without requiring replacement of failed cells or redundant battery cells. Such an apparatus is referred to below as a “fault tolerant” power supply system.